The control of insects, plant pathogens, nematodes and weeds is of central importance to the agriculture industry. In particular, the substantial reduction or elimination of nematode populations in soils is critical to initial plant growth, productivity and life-span. Pathogenic fungi and nematodes develop on the extensive root systems of both annual and perennial crops, damaging them severely. Moreover, they persist in the soil after crop removal and need to be eliminated before replanting of new crops.
Approaches which have been used successfully to combat plant pathogens and nematodes have been crop rotation, fallowing for at least four years, use of pathogen and nematode-resistant crops and soil fumigation. Resistance to plant pathogens and nematodes is available only in a few crops, and resistant cultivars may not be developed in the foreseeable future for many crops of significant commercial interest. Therefore, soil fumigation remains the best alternative for control of plant pathogens and nematodes.
Methyl bromide (CH3Br) is the most widely used and most universal fumigant in the world. It is used extensively for soil fumigation, as a commodity quarantine treatment (export and imports) to control a variety of pests on numerous crops, and as a structural fumigant for wood destroying pests.
Methyl bromide (hereinafter referred to as “MBr”) is categorized as an ozone depleting chemical with an ozone depleting potential (ODP) of greater than 0.2 compared to trichlorofluoromethane (cfc 11), a refridgerant used as a reference gas having an ODP of 1.
Evidence on the loss of MBr to the atmosphere after soil fumigation indicates that of the total amount applied to the soil for fumigation, approximately 87% is lost to the atmosphere within seven days. On reaching the stratosphere MBr undergoes photo-oxidation, releasing bromine atoms which enter the ozone depletion cycle. MBr loss from fumigated soils is further supported by studies which indicated a loss of as much as 70% of the applied MBr to the atmosphere through the tarp and after the tarp is removed.
As currently available alternatives to MBr are less effective and/or more expensive, the removal of MBr will be very costly. Annual losses to U.S. producers and consumers is estimated to be in the region of 1.5 billion dollars. This figure does not account for the losses due to post harvest and quarantine losses as well as structural fumigation losses. MBr removal would most adversely affect such commodities as tomatoes, strawberries, peppers, melons and ornamentals. The loss of MBr would thus be extremely costly to both agricultural producers and consumers as well as having a substantial impact on the U.S. economy. Nonetheless, it is the general consensus of those working in the field that no approach is currently available that will achieve the same level of broad-spectrum pest management as MBr; chemical and non-chemical approaches that are available can provide some level of agricultural pest management, but generally with narrower activity and lower crop yields and quality. Therefore, there is clearly a need for alternatives to MBr.